Gearboxes & gearbox design

How does a gearbox work?

What are Gearboxes?

Usually found near motors of some sort, gearboxes are used to reduce the load on the motor by using the motor's own momentum to keep it turning. Once a motor has reached a number of revolutions per minute, it is advisiable for the operator to increase the gear, to drop the revolutions on the motor, yet still keep the same amount of power created. This reduces wear on the engine, allows more control, and allows greater speeds.

Although, in practise, the main use of a Gearbox is to act as a reduction gear. These can be variable or non-variable, depending on the application. In other words, if when the motor is turning 2500 rpm the output shaft is turning 500, the gearbox is reducing the number of revolutions from input to output.

This is usually acheived by use of cog wheels. If the input shaft is connected to a small cog, the output shaft is connected to a large, and two are meshed together in the gear box, then it will take several turns of the input shaft to make the output turn once. This not only decreases wear on the motor, but also allows greater acceleration - infact the larger the reduction ratio, the larger the acceleration. Ever tried getting a car moving (from stationary) in it's 5th gear? There is simply not enough acceleration to move - therefore the engine will stall.

This lens will look at a few things associated with gearboxes, such as design, manufacture, how they work and similar pieces.

A Reduction Gear

Diagram of a reduction gear

Things that use gearboxes

There are a number of things that use gearboxes, however for ease we're going to split them up into 2 categories.

motors

engines

Motors are generally speaking electrical based, and require a battery of some description to work, furthermore, they usually either have an automatic gearbox, or that the user can switch between a selected number of gears (mainly forward, neutral and reverse), with the gearbox filling in the rest. Items such as electric wheelchairs, milk floats and golf buggies use electric motors with a semi automatic gearbox. Pumps, winches and bowling alley machines use electric motors with an automatic gearbox.

Engines are more likely to be run by a fuel, such as oil and are a lot larger, and more powerful, designed to be used for powering large systems. Most of them are manual, due to the range of conditions they need to use it (for example, how do you tell a computer to be in a lower gear for a hill?). As such, they are best used in things such as cars.

Perfect condition gearbox from a Yamaha YZ465 | Source

Gearbox Design

Gearbox design is a fairly difficult task, making sure that the designed and created gearbox is running at maximum efficiency for the task in hand. As such, we're unable to cover it here. Instead, here are some things you need to consider when designing a gearbox.

The Use - What are you using the gearbox for? Depending on whether the gearbox is used for a petrol engine or electric motor, it will vary the materials use and therefore the design.

The Materials You Have - Of course, the materials, gears and components you have access to can decide your design for you, making the best use of the equipment you have is vital.

The Space You Have - Finally, your gearbox will have to go somewhere so space limiations can be in force. Making the gearbox smaller than the space it goes into can have benefits on other parts of the system.